/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/Operations/SplitAttributeWelder.h
Welds split Normals / Tangents shared by the ParentVID vertex in the ParentMesh based on the angled between the vectors.
static void WeldSplitUnitVectors ( const int32 ParentVID, [FDynamicMeshNormalOverlay](API\Runtime\GeometryCore\DynamicMesh\TDynamicMeshVectorOverlay) & NormalOverlay, float DotThreshold, bool bMergeZeroVectors )